Acetic acid production process

Abstract

A method for determining the characteristic of one or more components in a step of an acetic acid production process using Raman spectroscopy. The process includes providing a feed stream comprising multiple components to a separations unit, one of the components being acetic acid, the separations unit separating the feed stream into two or more exit streams having a different composition from one another, and measuring a characteristic of one or more of the components by Raman spectroscopic analysis.

Description

FIELD OF THE INVENTION[0001]The present disclosure relates to monitoring components in an acetic acid preparation process. More particularly, the present disclosure relates to a method for measuring components by Raman spectroscopy in process steps downstream from an acetic acid reactor. Additionally, the disclosure relates to controlling an acetic acid production process in view of Raman spectroscopy measurements.BACKGROUND OF THE INVENTION[0002]Acetic acid is commercially produced by methanol carbonylation. Prior to 1970, acetic acid was made using a cobalt catalyst. A rhodium carbonyl iodide catalyst was developed in 1970 by Monsanto. The rhodium catalyst is considerably more active than the cobalt catalyst, which allows lower reaction pressure and temperature. Most importantly, the rhodium catalyst gives high selectivity to acetic acid.[0003]One problem associated with the original Monsanto process is that a large amount of water (about 14%) is needed to produce hydrogen in the ...

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Benefits of technology

[0011]The process and method disclosed herein includes determining the characteristic of one or more components in a step of an acetic acid production process. The method includes providing a feed stream having multiple components to a separations unit, one of the compon

Problems solved by technology

One problem associated with the original Monsanto process is that a large amount of water (about 14%) is needed to produce hydrogen in the reactor via the water-gas shift reaction (CO+H2OCO2+H2).

This large amount of water increases the amount of hydrogen iodide, which is highly corrosive and leads to engineering problems.

Further, removing a large amount of water from the acetic acid product is costly.

However, the high concentration of lithium iodide salt promotes stress crack corrosion of the reactor vessels.

Furthermore, the use of iodide salts increases the iodide impurities in the acetic acid product.

Several drawbacks regarding the use of infrared spectroscopy with acetic acid processes have been found as disclosed herein, including large H2O and acetic acid absorbance values while having relatively weak MeI absorbance values.

While large absorbances can be helpful in quantitation, in the acetic acid process, the absorbance values of H2O and acetic acid are so large that they have a tendency to overlap and interfere with absorbances of other components thereby making quantitation difficult.

Moreover, infrared has drawbacks regarding hardware flexibility and implementation in a process environment.

However, Raman spectroscopy has not been heretofore disclosed by academic or patent literature for use in acetic acid processes, except in pending application Ser. No.12 / 906,575, filed Oct. 18, 2010.

Accordingly, in an acetic acid process, it is unknown whether the components in the process will provide sufficiently observable spectra to determine concentration, and furthermore, in a multi-component system, some spectra may overlap therefore making observation difficult.

Therefore, it is unknown whether Raman spectroscopy can be employed in a multi-component system such as an acetic acid production process to accurately measure various components.

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